Ethyl lactate can be used, alone or in combination with other solvents, as cleaning and degreasing agents, in a washing machine and in a nonaqueous medium, for solid surfaces, such as metal components, ceramics, glass or plastics, which have been contaminated by machining oils or greases and/or for their temporary protection.
It can also be used for the defluxing of printed circuits, which operation consists in removing the soldering flux.
The methods most widely used industrially for producing ethyl lactate consist of an esterification reaction generally catalyzed by acids, according to the reaction:CH3CH(OH)CO2H+EtOH⇄CH3CH(OH)CO2CH2CH3+H2O  (1)
However, the implementation of this reaction is complicated due to the presence of a hydroxyl group on the lactic acid molecule.
Esterification can thus take place between two lactic acid molecules and can then continue to give lactic acid oligomers, according to the following schemes:
or

According to the operating conditions generally used, the lactide (IV) is not formed. On the other hand, the oligomers (II), (III) and/or (V) have been detected for the good reason that, industrially, commercial lactic acid solutions are used.
The term “lactic acid composition” is understood now to mean any aqueous lactic acid solution, whatever its process of preparation and its characteristics, said solution having a highly variable lactic acid purity.
Commercially available solutions comprising 50, 80, 87 or 90% of organic compounds may in particular be concerned, it being understood that such solutions are in fact mixtures of water, of monomers, of dimers and of higher oligomers of lactic acid.
Thus, in order to productively manufacture ethyl lactate (I), it is necessary not only to esterify the lactic acid monomer but also to depolycondense the oligomers of lactic acid.
Otherwise, oligomers of ethyl lactate are obtained by esterification of the oligomers of lactic acid, according to the reaction:CH3CH(OH)CO2[CH(CH3)CO2]nH+C2H5OH→CH3CH(OH)CO2[CH(CH3)C(O)]nOC2H5+H2O  (6)
Consequently, in order to minimize, indeed even eliminate, the formation of the oligomers of ethyl lactate originating from the reaction (6), it is necessary to use a large excess of ethanol and use is generally made of an ethanol/lactic acid molar ratio at least equal to 2.5.
Furthermore, it should be noted that, during the purification of the crude ethyl lactate obtained by esterification of lactic acid with ethanol, a transesterification reaction between two ethyl lactate molecules can occur, according to the reaction:

This transesterification reaction (7) is generally carried out in the presence of basic catalysts, of alkyl orthotitanates or of zirconium-based complexes.
However, it can also take place by heating during the purification of the ethyl lactate and, in order to prevent it, the purification is generally carried out under reduced pressure.
Thus, the esterification of lactic acid to give ethyl lactate is rendered more complicated by:                the presence of oligomers of lactic acid in the starting lactic acid compositions, which it is a matter of depolycondensing in order to obtain the lactic acid,        the competition between the expected esterification (lactic acid, ethanol) and two esterifications which result in the formation of ethyl lactate oligomer (one esterification between lactic acid and ethyl lactate, another between ethanol and an oligomer of lactic acid).        
In addition, Applicants have found that it is possible to form a water/ethyl lactate binary azeotrope, thus complicating the removal of the water from the ethyl lactate.
It is therefore necessary to produce, during the esterification of lactic acid by ethanol, an ethyl lactate having a water content which is as low as possible in order to subject it to a purification consisting of a distillation under reduced pressure.
Consequently, in order to remove the water formed according to the main reaction (1) and optionally according to the reactions (2) and (3) of the esterification reaction medium comprising a mixture of lactic acid, of ethanol, of ethyl lactate, of water and of oligomers, the simplest method is to use the water/ethanol azeotrope.
However, this results in an ethanol/water mixture which cannot be directly recycled in the reaction medium and, consequently, results in an esterification process which is not very economic industrially.
To achieve this, it is therefore necessary to carry out the separation of the water from the ethanol by a technique other than distillation.
In U.S. Pat. No. 5,723,639, the water is selectively removed from the reaction medium by conveying it through a pervaporation membrane.
However, it is expensive to operate in this way, this operation using a technology not employed to any great extent in the basic chemical industry.